Since its first flight back in February, Boeing's biggest-ever aircraft, the 747-8, has been undergoing intensive flight testing, some of which is quite extreme. "Some people may even call it abusive," says Mark Feuerstein, Boeing's chief test pilot for the big freighter. "It certainly requires a lot of forethought to execute some of the maneuvers." One of the more challenging tests requires the crew to drag the airplane's tail along a runway, which is somewhat tricky. "It's a balance between being forceful and being gentle," says Feuerstein. "We want to be forceful to get the plane's tail moving down towards the runway, but of course we want to be very gentle when we set the tail down." The maneuver, known as the velocity minimum unstick test, is critical to determine the lowest speed at which the freighter can take off, Boeing said.

Boeing has four 747-8 freighters flying in its test program. So far they have logged about 1,500 flight hours and have to fly about 1,500 more to achieve certification. Tests so far completed include ground-effect studies, stability and control checks, and stalls. "Usually in most of the stalls that I've flown, I merely relax back pressure on the column to neutral column and the airplane recovers just fine," said Feuerstein. The test pilots intentionally excite or pulse the wing and other control surfaces to make sure the airplane can dampen the vibrations. One of the aircraft flew at a gross weight of 1,010,000 pounds, the heaviest takeoff in Boeing history. While delays in Boeing's 787 program have been widely reported, the 747-8 freighter has attracted less attention. Ten of the freighters have already been assembled, and deliveries are expected to start sometime in 2011. A passenger version is expected to start flight tests within the next few months. Boeing has about a hundred orders for the big jet, about three-quarters of them for the freighter version.